This invention relates to coated glass fiber bundles suitable for rubber reinforcement.
It has been long recognized that glass fiber material makes an ideal reinforcement for rubber products, such as automobile tires and the like. In preparing glass fiber material for such applications, the individual glass fibers and groups of glass fibers in the form of strand, rope, cord, roving, fabric and the like, are coated with a rubber adhesive to aid in bonding the glass to the elastomeric materials to be reinforced. The rubber adhesive generally comprises a resin and an elastomeric material to link between the glass and the main body of material being reinforced.
Generally, in the production of fiber glass reinforcing cords or other bundle forms, individual fibers are coated with a size and then are brought together in bundle form. The bundle is coated by dipping or otherwise contacting with a coating mixture containing an elastomeric latex and a homogeneous resin component. Commonly, the sizing contains a coupling agent, such as a silane or Werner complex, a lubricant, and other ingredients to assist in handling the cord during processing.
Glass fibers are excellent reinforcing materials and are distinguishable from other fibrous reinforcing materials such as natural and synthetic organic fibers, in that glass fibers do not become elongated or deformed under stress to the extent of other fibers. Unlike other fibers, particular combinations of glass fibers with encapsulating coatings cooperate to yield reinforced materials that have greater strength than either the glass or the coating material alone. While fibrous materials, other than glass, which are subject to substantial stress elongation, are essentially limited in tensile strength to the basic strength of the bare fibers, even if coated, properly coated glass fibers have greater strength than the glass alone. For example, the low modulus elasticity of glass may be exploited to provide reinforced tires having superior road performance if an appropriate coating medium is provided to transfer stresses to all fibers in the glass fiber cord so that loading throughout is substantially uniform. This phenomenon is illustrated by the observation that a typical uncoated fiber glass cord (G75, 5/0, filament count 2,000 i.e., 2,000 filaments of G fibers of about 9.14.mu. meters diameter, 15,120 meters/kg., five strands per cord) has a tensile strength of about 35 to 40 pounds (156 to 178 newtons) ASTM test G 578-52 but when coated with the resorcinol formaldehyde latex coating, such a cord has a tensile strength of about 50 to 70 pounds (222 to 311 newtons).
The above mentioned coated glass fiber cord, the G-75, 5/0 has found particular utility in the reinforcement of power transmission belts and fiber glass reinforced tires and the like. However, to date, glass fiber tire cord has found its main utility in bias belted tires. It is the desire of the pneumatic tire industry to produce radial tires reinforced with glass fibers which would have extended mileage, improved handling, and the like properties over the bias belted tires. However, the typical glass fiber tire cord, G-75, 5/0 shows some deficiency in use with radial ply tires.
In a radial tire, just as in bias ply tires, the carcass is reinforced with a reinforcing cord such as nylon, rayon, steel, glass or the like. However, in radial tires, as opposed to bias belted tires, the amount of cord necessary for reinforcement is much greater. Because of this, it is necessary to incorporate more individual filaments per unit area in the carcass and belt in order to incorporate more individual filaments per unit area, i.e., the packing of the cord must be greater. It has been found that in order to facilitate in maintaining the necessary packing, a thicker cord is required, and cords having from 10 to 15 strands therein have been found to have utility for this purpose. However, this cord, with more strands therein, produces an effect known as blow holes. A blow hole is caused when cord is cured within the rubber matrix and the individual strands which comprise the cord have greater adhesion to the rubber matrix than cohesion to themselves. Therefore, the strands separate and pull apart, thus inducing an air space between the individual strands in the cord. This blow hole phenomenon detracts from the desirable properties which are imparted by radial ply tires. Therefore, there is a need for an improved coating composition to reduce or completely obviate this blow hole phenomenon.
In accordance with the invention, a glass fiber coating composition is provided, which when coated on fiber strand which is subsequently plied into cords and incorporated into an elastomeric matrix, which substantially reduces or completely obviates this blow hole phenomenon.